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Comparison of the Properties of Activated Carbons Produced in One-Stage and Two-Stage Processes

1
Research Unit of Sustainable Chemistry, University of Oulu, P.O. Box 3000, FI-90014 Oulu, Finland
2
Unit of Applied Chemistry, University of Jyvaskyla, Kokkola University Consortium Chydenius, Talonpojankatu 2B, FI-67100 Kokkola, Finland
*
Author to whom correspondence should be addressed.
Received: 11 June 2018 / Revised: 5 July 2018 / Accepted: 6 July 2018 / Published: 16 July 2018
(This article belongs to the Special Issue Carbons from Biomasic Waste and Their Applications)
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Abstract

Activated carbons (ACs) can be produced from biomass in a thermal process either in a direct carbonization-activation process or by first carbonizing the biomass and later activating the bio-chars into activated carbons. The properties of the ACs are dependent on the type of process used for production. In this study, the properties of activated carbons produced in one-stage and two-stage processes are considered. Activated carbons were produced by physical activation of two types of starting materials: bio chars produced from spruce and birch chips in a commercial carbonization plant and from the corresponding raw chips. The activated carbons produced were characterized regarding specific surfaces, pore volumes, and pore size distributions. The un-activated bio chars had varying surface areas, 190 and 140 m2 g−1 for birch and spruce, respectively, and pore volumes of 0.092 and 0.067 cm3 g−1, respectively. On the other hand, 530–617 and 647–679 m2 g−1 for activated bio chars from birch and spruce, respectively, and pore volumes 0.366–0.509 and 0.545–0.555 cm3 g−1, respectively, were obtained. According to the results obtained, two slightly different types of activated carbons are produced depending on whether a one-stage or a two-stage carbonization and activation process is used. The ACs produced in the one-stage process had higher specific surface areas (SSA), according to the BET-model (Brunauer–Emmett–Teller), compared to the ones produced in a two-stage process (761–940 m2 g−1 vs. 540–650 m2 g−1, respectively). In addition, total pore volumes were higher in ACs from the one-stage process, but development of micro-pores was greater compared to those of the two-stage process. This indicates that the process can have an influence on the ACs’ porosity. There was no significant difference in total carbon content in general between the one-stage and two-stage processes for spruce and birch samples, but some differences were seen between the starting materials. Especially in the one-stage procedure with 2 and 4 h steam activation, there was nearly a 10% difference in carbon content between the spruce and birch samples. View Full-Text
Keywords: biomass; bio-char; activation; activated carbon; thermal treatment; physical activation; porosity; specific surface areas biomass; bio-char; activation; activated carbon; thermal treatment; physical activation; porosity; specific surface areas
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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MDPI and ACS Style

Bergna, D.; Varila, T.; Romar, H.; Lassi, U. Comparison of the Properties of Activated Carbons Produced in One-Stage and Two-Stage Processes. C 2018, 4, 41.

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